The present invention relates to a piezoelectric fluid control valve which is the fluid control valve opened and closed by piezoelectric elements and more specifically to a normally opened piezoelectric fluid control valve in which an open state of the valve is maintained in non-operation.
A piezoelectric fluid control valve which is a fluid control valve opened and closed by a piezoelectric element laminate formed by laminating a plurality of piezoelectric elements is known as disclosed in Japanese Patent Application Laid-open No. 11-173440, for example. This fluid control valve is of a type in which a valve member is opened and closed by using expanding and contracting forces of the piezoelectric element laminate, has an advantage that large operating force can be obtained, and is generally formed as a normally closed type. In the normally closed fluid control valve, a closed state of the valve member is maintained by repulsing force of a valve spring in non-operation when the piezoelectric element laminate is not energized and the valve spring is compressed by expanding force of the piezoelectric element laminate to open the valve member when the piezoelectric element laminate is energized.
However, because a normally opened fluid control valve is advantageous in some cases depending on use of the fluid control valve, the fluid control valve having a normally opened structure is also proposed. In Japanese Patent Application Laid-open No. 11-108227, an example of such a normally opened fluid control valve is disclosed. This example is of a type in which a valve seat is opened and closed with a metal diaphragm valve. In non-operation when a piezoelectric element laminate is not applied with a voltage, the piezoelectric element laminate is displaced in such a direction as to separate from the metal diaphragm valve by repulsing force of a return spring and, as a result, the metal diaphragm valve opens the valve seat with its own elastic force. When the piezoelectric element laminate is applied with the voltage, the piezoelectric element laminate compresses the return spring with its expanding force to press the metal diaphragm valve against the valve seat.
However, because the diaphragm valve is directly pressed against the valve seat by the large expanding force of the piezoelectric element laminate in the prior-art normally opened fluid control valve as described above, the diaphragm valve and the valve seat are likely to be deformed or damaged and there are problems with durability and safety.
It is a technical object of the present invention to provide a normally opened piezoelectric fluid control valve with a rational design structure and excellent durability in which valve closing force can be obtained by repulsing force of a spring by converting expanding force of a piezoelectric element laminate into the repulsing force of the spring.
To achieve the above object, according to the present invention, there is provided a piezoelectric fluid control valve comprising a valve mechanism portion for opening and closing a fluid flow path by displacement of a diaphragm valve and a piezoelectric operating portion for opening and closing the diaphragm valve. The valve mechanism portion includes in a first casing the fluid flow paw path, a valve seat provided in the fluid flow path, the diaphragm valve for coming in contact with and separating from the valve seat to open and close the fluid flow path, and a pressing member in contact with a back face of the diaphragm valve. The piezoelectric operating portion includes in a second casing a piezoelectric element laminate for expanding due to application of a voltage, a first member for transmitting expanding force of the piezoelectric element laminate to the pressing member to seat the diaphragm valve on the valve seat, a spring seat displaced with a second member in expansion of the piezoelectric element laminate, and a valve spring elastically deformed by displacement of the spring seat, and a distortion amount of the piezoelectric element laminate in expansion is set at such a value as to press the pressing member to seat the diaphragm valve on the valve seat and as to press the spring seat in a reverse direction to elastically deform the valve spring.
In the fluid control valve of the invention having the above structure, in non-operation, the diaphragm valve separates from the valve seat due to its own elastic force to maintain an open state of the valve. If a certain amount of voltage is applied to the piezoelectric element laminate in this state, the piezoelectric element laminate expands in an axial direction, pushes the pressing member to seat the diaphragm valve on the valve seat, and pushes the spring seat in the reverse direction to elastically deform the valve spring. As a result, the repulsing force of the valve spring acts on the diaphragm valve through the piezoelectric element laminate and the diaphragm valve is pressed against the valve seat by the repulsing force. In other words, expanding force of the piezoelectric element laminate is converted into the repulsing force of the valve spring and the force for seating the diaphragm valve is obtained by the repulsing force. Therefore, because the large expanding force of the piezoelectric element laminate does not directly act on the diaphragm valve and the valve seat, the diaphragm valve and the valve seat are not deformed or damaged and durability and safety are improved.
According to a preferable concrete embodiment of the invention, the first casing and the second casing are connected to each other with an end of the second casing fitted in a valve hole of the first casing, an outer peripheral portion of the diaphragm valve is airtightly sandwiched and fixed between a tip end portion of the second casing and a peripheral bottom portion of the valve hole, and the pressing member is retained for displacement in the second casing.
According to another concrete embodiment of the invention, the spring seat is mounted such that a position of the spring seat can be adjusted by using an adjusting screw and the adjusting screw is displaced by the second member.
It is preferable in the invention that the second casing of the piezoelectric operating portion has a first stopper to which the pressing member is locked to thereby restrict an opening stroke end of the diaphragm valve when the piezoelectric element laminate is not energized and a second stopper to which the spring seat is locked to thereby restrict an expanding end of the valve spring.
In the invention, it is possible that the pressing member and the first member are in contact with each other through a ball fitted in depressions formed at centers of opposed faces.
According to another concrete embodiment of the invention, the first casing has on an end face thereof opposite to a side connected to the second casing a mounting face to be mounted to a unit substrate and a plurality of fluid ports communicating with the fluid flow path are provided to the mounting face.